The present invention relates to an attachment lens device to be inserted between a master lens and a camera body, and an imaging apparatus incorporating the same.
So far, there has been an attachment lens device known in the art that can be attached between an assortment of interchangeable lenses, each providing a master lens, and a camera body, and comprises a focusing lens group to be moved for the purpose of implementing focusing.
For instance, JP(A) 58-43415 discloses an attachment lens device having a lens movable in the optical axis direction, wherein the focusing of a combined master lens/attachment lens device optical system is implemented by movement of lenses in the attachment lens device.
JP(A) 8-286109 discloses an apparatus designed to implement focusing by both a master lens and an attachment lens device, thereby making a focusable area wider.
JP(A) 1-284811 discloses an attachment lens device that, when focusing by a focusing lens group in a master lens is less than satisfactory, is actuated to move a focusing lens group in it for focusing purposes.
Recently for a camera designed to take moving or still images, reliance has often been on a contrast type focusing mode wherein a focusing lens group in an assortment of interchangeable lenses used with that camera is moved to detect an in-focus peak where there is the highest contrast obtained.
For interchangeable lenses that implement focusing operation in the contrast mode, there has been a technical method known wherein a focusing lens group is finely vibrated (wobbled) in the optical axis direction, and then moved on the basis of a contrast change for focusing, thereby boosting up focusing speed and/or focusing precision.
With an interchangeable lens having none of the aforesaid wobbling capability, an operator may miss out on right timings because there is an extension of movement of the focusing lens group, which may otherwise render out-of-focusing time longer upon focusing operation.
Nowhere in JP(A) s 58-43415, 8-286109 and 1-284811 is wobbling mentioned; even when an interchangeable lens having no wobbling capability is used to implement focusing on a contrast readings basis, it is impossible to achieve sufficiently fast focusing operation.